Our invention relates to the placement of a column of sand in the wellbore of an oil, gas, or other fluid producing well. Such wellbores typically have production casing which is perforated at depths adjacent to producing formations. The conventional well completion will have tubing within the production casing, although current practices include completions which utilize the casing without tubing. Tubingless completions will typically use a smaller internal diameter pipe for the casing.
In a number of applications, in the oil and gas industry, the operator will need to place a sand column over a particular interval in the wellbore, e.g. isolating producing zone perforations in the production casing string, isolating and enhancing the integrity of a bridge plug, temporarily abandoning the well, and other applications. Such a sand column fills the wellbore from one depth to another. These applications will typically involve a column of salt water in the wellbore, the water being used to overcome the formation pressure and keep hydrocarbons from entering the wellbore during the operation.
The salt water typically encountered in these situations include lease water (produced), heavy NaCl brines, fresh water with KCl additives for formation protection, and other solutions with varying densities. Although more exotic solutions have higher densities, e.g. some calcium chlorides, zinc bromides, and calcium Bromide solutions, it remains that, in the vast majority of situations, the wellbore will contain salt water solutions with densities ranging from that of fresh water to about twelve pounds per gallon.
Current methods of placing the sand in the desired wellbore interval primarily involve the use of sand bailers, which are run into the wellbore by wireline. This can be a costly and time-consuming process, depending on the depth of the well, the height of the desired sand column, and other factors. Furthermore, it requires the temporary insertion of substantial hardware into the wellbore, creating an opportunity for mechanical failure and the possibility of lost tools which must be fished at high expense. Without the sand bailer, the operator is limited to dropping sand into the wellbore, although this is very impractical due to possible "bridging" of the sand while descending, as well as, the time required for the unconsolidated sand to descend to the desired depth.
Another method involves pumping a high-viscosity, liquid slurry of sand and polymer, down the tubing into a pressure isolated area adjacent to the production casing perforations. The operator must first fill the tubing with a liquid, typically salt water, and this volume of tubing liquid enters the formation before the slurry reaches its desired position. Such foreign fluid entry into the formation has potentially undesirable effects. After the slurry reaches the desired location, it is allowed to set, and is then pressure tested to see if the perforations are adequately isolated from fluid flow, by the slurry.
Another unsatisfactory method of placing sand is to drop unconsolidated sand into the tubing or casing at the surface. This is not feasible when the well has surface pressure, and is highly conducive to "bridging" when the sand accumulates at locations higher than the effective bottom of the well.
The ability to quickly place a column of sand in a wellbore, without utilizing the above methods, is very desirable and is the subject of our invention.